Semiconductor device and dc-to-dc converter

ABSTRACT

In general, according to one embodiment, a semiconductor device includes a device main body, a semiconductor substrate. The device main body includes a semiconductor substrate mounting part and a first conductor provided around the semiconductor substrate mounting part. The semiconductor substrate includes a DC-to-DC converter control circuit having a detector to detect at least one of a current flowing through the first conductor and a voltage supplied to the first conductor. The semiconductor substrate is disposed on the semiconductor substrate mounting part so that the detector comes close to the first conductor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of application Ser. No. 12/883,627 filed Sep. 16, 2010; the entire contents of which are incorporated herein by reference.

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-295981, filed on Dec. 25, 2009; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device and DC-to-DC converter.

BACKGROUND

Switching circuits having switch elements, such as a DC-to-DC converter, for example, have been employing a higher and higher switching frequency to meet the demand for fast response to load change. Further, a parasitic capacitance of a switch element which drives an inductor has been increased with the increase in output current.

In such a switching circuit, ringing tends to occur at both rising and falling edges where an output current or an output voltage changes. Therefore, a usable switching frequency is limited by the time when the ringing converges, and is thus limited by a parasitic capacitance and a parasitic inductance of wiring or the like.

Generally, a semiconductor chip provided with such a switching circuit is mounted and packaged on a lead frame. The semiconductor chip is mounted in the center of the lead frame regardless of the chip size. Further, there is also known a chip-stacked semiconductor device having multiple semiconductor chips stacked and mounted on a substrate to reduce the substrate area. In the case of a semiconductor device of this type in which first and second semiconductor chips are stacked on the substrate, the first semiconductor chip is disposed with a virtual central axis of the first semiconductor offset from the center of the substrate (for example, refer to JP-A 2005-26564 (Kokai)).

However, the package structure as described above has difficulty in reducing the parasitic inductance and the like, and is limited in increasing the usable switching frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view illustrating a configuration of a semiconductor device according to the embodiment;

FIG. 2 is a circuit diagram illustrating a DC-to-DC converter including the semiconductor device shown in FIG. 1.

FIGS. 3A and 3B are current waveform diagrams of the first switch element;

FIG. 4 is a circuit diagram illustrating a DC-to-DC converter according to another embodiment; and

FIG. 5 is a circuit diagram illustrating a DC-to-DC converter according to another embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor device includes a device main body, a semiconductor substrate. The device main body includes a semiconductor substrate mounting part and a first conductor provided around the semiconductor substrate mounting part. The semiconductor substrate includes a DC-to-DC converter control circuit having a detector to detect at least one of a current flowing through the first conductor and a voltage supplied to the first conductor. The semiconductor substrate is disposed on the semiconductor substrate mounting part so that the detector comes close to the first conductor.

With reference to the drawings, embodiments are described in detail below. The drawings are schematic and conceptual; and shapes of respective portions, relationships between horizontal and vertical dimensions thereof, the proportions of sizes among portions, and the like are not necessarily the same as the actual values thereof. Further, the dimensions and proportions may be illustrated differently among drawings, even for identical portions. In the specification of this application and drawings, components similar to those described previously with reference to earlier drawings are marked with like reference numerals, and a detailed description is omitted as appropriate.

FIG. 1 is a schematic plan view illustrating a configuration of a semiconductor device according to the embodiment.

As shown in FIG. 1, a semiconductor device 1 includes a semiconductor substrate 2 and a device main body 3.

On the semiconductor substrate 2, a DC-to-DC converter control circuit 30 is provided. The DC-to-DC converter control circuit 30 has a detector 16. The semiconductor substrate 2 has four sides.

On the semiconductor substrate 2, a terminal BOOT, a power supply terminal VIN, a first terminal LX, and a ground terminal GND are provided on a first side 5. Terminals VFB, COMP, EN and SS are provided on the opposite side to the first side 5. The power supply terminal VIN, the first terminal LX and the ground terminal GND are connected to the detector 16. The terminals BOOT, VFB, COMP, EN and SS are connected to the DC-to-DC converter control circuit 30.

The device main body 3 includes: a semiconductor substrate mounting part 4 for mounting the semiconductor substrate 2; and first conductors K2 to K4 and second conductors K1 and K5 to K8, which are provided around the semiconductor substrate mounting part 4. The first and second conductors K1 to K8 have multiple pins P1 to P8, wires H1, first wires H2 to H4, and wires H5 to H8.

The pins P2 to P4 of the first conductors K2 to K4 are portions through which at least one of a current and a voltage is supplied to the first conductors K2 to K4 from the opposite side to the semiconductor substrate 2. Moreover, the pins P1 and P5 to P8 of the second conductors K1 and K5 to K8 are portions through which a signal is inputted to or outputted from the second conductors K1 and K5 to K8 from the opposite side to the semiconductor substrate 2.

A virtual center line DL of the semiconductor substrate 2 is disposed to be offset to the first side 5 by an offset amount DW with respect to a virtual center line IL of the semiconductor substrate mounting part 4. Note that FIG. 1 illustrates the configuration in which the device main body 3 has the first and second conductors K1 to K8 on both sides of the semiconductor substrate mounting part 4. However, first and second electrodes may be provided around the semiconductor substrate mounting part 4.

The terminal BOOT and the pin P1 are connected by the wire H1. The pin P1 and the wire H1 make up the second conductor K1. The terminal BOOT serves as a connection part between the second conductor K1 and the semiconductor substrate 2.

The power supply terminal VIN and the pin P2 are connected by the first wire H2. The pin P2 and the first wire H2 make up the first conductor K2. The power supply terminal VIN serves as a connection part between the first conductor K2 and the semiconductor substrate 2. The first terminal LX and the pin P3 are connected by the second wire H3. The pin P3 and the second wire H3 make up the first conductor K3. The first terminal LX serves as a connection part between the first conductor K3 and the semiconductor substrate 2. The ground terminal GND and the pin P4 are connected by the third wire H4. The pin P4 and the third wire H4 make up the first conductor K4. The ground terminal GND serves as a connection part between the first conductor K4 and the semiconductor substrate 2.

The terminal VFB and the pin P5 are connected by the wire H5. The pin P5 and the wire H5 make up the second conductor K5. The terminal COMP and the pin P6 are connected by the wire H6. The pin P6 and the wire H6 make up the second conductor K6. The terminal EN and the pin P7 are connected by the wire H7. The pin P7 and the wire H7 make up the second conductor K7. The terminal SS and the pin P8 are connected by the wire H8. The pin P8 and the wire H8 make up the second conductor K8.

The first wires H2 to H4 and the wires H1 and H5 to H8 are made of, for example, bonding wires, metal sheets or the like.

As described above, the virtual center line DL of the semiconductor substrate 2 is disposed to be offset to the first side 5 with respect to the virtual center line IL of the semiconductor substrate mounting part 4. Thus, the wire H1 and the first to third wires H2 to H4 are shorter than the wires H5 to H8.

In other words, the semiconductor substrate 2 is disposed on the semiconductor substrate mounting part 4 so that the detector 16 comes close to the first conductors K2 to K4. Accordingly, the first conductors K2 to K4 are shorter than they are when the semiconductor substrate 2 is disposed in the center of the semiconductor substrate mounting part 4.

Moreover, the semiconductor substrate 2 is disposed on the semiconductor substrate mounting part 4 so that the detector 16 comes closer to the first conductors K2 to K4 than to the second conductors K5 to K8.

Note that FIG. 1 shows a state of the semiconductor device during assembly thereof, in which the pins P1 to P8 are connected to each other. When the semiconductor device 1 is used after completion of the assembly thereof, connections among the pins P1 to P8 are cut off.

FIG. 2 is a circuit diagram illustrating a DC-to-DC converter including the semiconductor device shown in FIG. 1.

As shown in FIG. 2, a DC-to-DC converter 6 includes the semiconductor device 1, a first inductor 7, a first capacitor 8, a feedback circuit 9 and capacitors 11 to 13.

One end of the first inductor 7 is connected to the pin P3 of the semiconductor device 1 and connected to the first terminal LX through the second wire H3. In other words, the one end of the first inductor 7 is connected to an output of the DC-to-DC converter control circuit 30 through the first conductor K3.

Between the other end of the first inductor 7 and the ground, the first capacitor 8 and the feedback circuit 9 are connected in parallel. Further, a load circuit 10 is connected between the other end of the first inductor 7 and the ground, and an output voltage Vout is outputted to the load circuit 10. The feedback circuit 9 has a voltage-dividing resistor and feeds back a voltage obtained by dividing the output voltage Vout to the second conductor K5, i.e. the pin P5 of the semiconductor device 1. Note that while the voltage obtained by dividing the output voltage Vout is fed back to the pin P5 in FIG. 2, the output voltage Vout may be fed back to the pin P5.

The capacitor 11 is connected between the second and first conductors K1 and K3 of the semiconductor device 1, i.e. between the pins P1 and P3 thereof. The capacitor 12 is connected between the second conductor K6, i.e. the pin P6 of the semiconductor device 1 and the ground. The capacitor 13 is connected between the second conductor K8, i.e. the pin P8 of the semiconductor device 1 and the ground. Moreover, a power-supply voltage is supplied to the first conductor K2, i.e. the pin P2 of the semiconductor device 1, and the first conductor K4, i.e. the pin P4 of the semiconductor device 1 is connected to the ground. Further, a capacitor 23 is connected as a bypass capacitor between the pin P2 and the ground, and the pin P2 is connected to the ground in respect of alternating currents. An enable signal is inputted to the second conductor K7, i.e. the pin P7 of the semiconductor device 1. Functions of the respective pins P1 to P8 of the semiconductor device 1 are described later.

The DC-to-DC converter 6 steps down the power-supply voltage supplied to the semiconductor device 1 to the output voltage Vout.

The DC-to-DC converter control circuit 30 further includes a first switch element Q1, a second switch element Q2 and a controller 14, which are provided on the semiconductor substrate 2.

The first switch element Q1 has one end connected to the power supply terminal VIN and the other end connected to the first terminal LX. The second switch element Q2 has one end connected to the first terminal LX and the other end connected to the ground terminal GND.

As described above, the power supply terminal VIN, the first terminal LX and the ground terminal GND are connected to the first conductors K2 to K4, respectively, i.e. connected to the pins P2 to P4 in the device main body 3, respectively, through the first to third wires H2 to H4. These first to third wires H2 to H4 are electrically equivalent to a parasitic inductance. Note that cross-sectional areas of the pins P2 to P4 are much larger than those of the first to third wires H2 to H4, and inductances of the pins P2 to P4 are much smaller than those of the first to third wires H2 to H4. Therefore, inductances of the first conductors K2 to K4 are approximately equal to those of the first to third wires H2 to H4. The same goes for the second conductors K1 and K5 to K8.

The pins P2 and P4 are connected to an external power supply and the ground, respectively, and the power-supply voltage is supplied between the pins P2 and P4 as described above.

The first and second switch elements Q1 and Q2 are controlled between ON and OFF states by the controller 14, respectively. When the first switch element Q1 is in the ON state and the second switch element Q2 is in the OFF state, the first terminal LX is connected electrically to the power supply terminal VIN. On the other hand, when the first switch element Q1 is in the OFF state and the second switch element Q2 is in the ON state, the first terminal LX is connected electrically to the ground terminal GND.

The controller 14 includes a driver 15, the detector 16, a voltage generator 17, an error amplifier 18, a comparator 19 and a current generator 20.

The driver 15 drives the first and second switch elements Q1 and Q2 between the ON and OFF states so that the voltage fed back to the terminal VFB, i.e. the output voltage Vout becomes constant. The detector 16 is a current detector which is connected to the power supply terminal VIN, the first terminal LX and the ground terminal GND, and detects, through the first conductors K2 to K4, a current flowing through the first switch element Q1. The detector 16 detects an output current of the DC-to-DC converter control circuit 30 by detecting the current flowing through the first switch element Q1. The detector 16 includes a detecting transistor, a resistor and a differential amplifier.

The voltage generator 17 is a circuit for generating a reference voltage, and is set according to the output voltage Vout. The error amplifier 18 amplifies an error between the voltage inputted to the terminal VFB and the reference voltage generated by the voltage generator 17. The error amplifier 18 is connected to the terminal COMP and connected to the pin P6 through the wire H6. Further, the capacitor 12, for example, is connected to the pin P6 for phase compensation. Note that other circuit configurations are possible for phase compensation.

The comparator 19 has a positive input terminal and two negative input terminals. An output of the detector 16 is inputted to the positive input terminal. An output of the error amplifier 18 is inputted to one of the negative input terminals. The other negative input terminal is connected to the current generator 20 and the terminal SS, and also connected to the pin P8 through the wire H8. For example, the capacitor 13 is further connected to the pin P8. The current generator 20 and the capacitor 13 make up a soft start circuit to control the output voltage Vout at start-up.

The capacitor 13 in its steady state is charged to a fixed potential by the current generator 20. The comparator 19 compares the output of the detector 16 with the output of the error amplifier 18. The comparator 19 outputs a high level when the voltage inputted to the terminal VFB is lower than the reference voltage, and otherwise outputs a low level.

When the output from the comparator 19 is the low level, the driver 15 performs control to extend the ON-state period of the first switch element Q1. On the other hand, when the output from the comparator 19 is the high level, the driver 15 performs control to shorten the ON-state period of the first switch element Q1.

Moreover, the driver 15 is connected to the terminal EN, and connected to the pin P7 through the second conductor K7, i.e. the wire H7. As described above, the enable signal is inputted to the pin P7 from the outside. When the enable signal is at a high level, the driver 15 is set in a normal operation mode for turning on and off the first and second switch elements Q1 and Q2. On the other hand, when the enable signal is at a low level, the driver 15 is set in a standby mode for controlling the first and second switch elements Q1 and Q2 to be set in the OFF state.

The driver 15 is also connected to the terminal BOOT, and connected to the pin P1 through the second conductor K1, i.e. the wire H1. Further, the capacitor 11, for example, is connected between the pins P1 and P3. When the first switch element Q1 is in the OFF state, a current is supplied to the pin P3 through the capacitor 11.

In this way, the DC-to-DC converter control circuit 30 of the semiconductor device 1 uses the controller 14 to control the voltage fed back to the terminal VFB to be constant by turning on and off the first and second switch elements Q1 and Q2. Accordingly, the output voltage is controlled to be constant by the controller 14.

Note that FIG. 2 illustrates the configuration in which the semiconductor device 1 has the second switch element Q2. However, the second switch element Q2 may be replaced by a rectifying element connected so that a current flows in a direction from the ground terminal GND to the first terminal LX.

As described above, the semiconductor device 1 generates, at the output of the DC-to-DC converter control circuit 30, i.e. at the first terminal LX connected to the pin P3, a voltage switched between a power supply potential and a ground potential by turning on and off the first and second switch elements Q1 and Q2.

As described above, between the pin P2 and the power supply terminal VIN where the power is supplied, there is a parasitic inductance generated by the first wire H2. Between the pin P3 and the first terminal LX, there is a parasitic inductance generated by the second wire H3. Between the pin P4 connected to the outside ground and the ground terminal GND, there is a parasitic inductance generated by the third wire H4.

Also, there is a parasitic capacitance between a drain and a back gate of each of the first and second switch elements Q1 and Q2. FIG. 2 equivalently shows a parasitic capacitance 21 connected between the first terminal LX and the ground terminal GND.

As the output current is increased, areas of the first and second switch elements Q1 and Q2 are increased, and a capacitance C of the parasitic capacitance 21 is also increased.

In the voltage generated at the first terminal LX, ringing occurs at both of a rising edge where the voltage changes from the ground potential to the power supply potential and a falling edge where the voltage changes from the power supply potential to the ground potential. Moreover, ringing also occurs in the current flowing through the first and second switch elements Q1 and Q2.

A ringing frequency f0 is expressed by the following formula (1) with the parasitic inductance L and the capacitance C of the parasitic capacitance 21.

$\begin{matrix} {{f\; 0} = \frac{1}{2\; \pi \sqrt{LC}}} & (1) \end{matrix}$

The larger the parasitic inductance L and the larger the capacitance C of the parasitic capacitance 21, the longer the ringing cycle. Therefore, the larger the output current, the longer it takes to attenuate and stabilize the ringing of the current.

Accordingly, as the parasitic inductance L and the capacitance C of the parasitic capacitance 21 are increased, it takes longer to stabilize the output of the detector 16.

Incidentally, the parasitic inductance L is approximately proportional to a length of a wire connecting the semiconductor substrate 2 to a lead frame 3.

Table 1 shows, for example, a relationship between a wire length and an offset amount DW of the center DL of the semiconductor substrate 2 with respect to the lead frame 3.

TABLE 1 Wire length (mm) Pin Terminal DW = 0 μm DW = 600 μm P1 BOOT 1.74 1.29 P2 VIN 1.58 0.99 P3 LX 1.58 0.99 P4 GND 1.43 0.98 P5 VFB 1.76 2.28 P6 COMP 1.43 2.03 P7 EN 1.43 2.03 P8 SS 1.76 2.28

In Table 1, the first column indicates the pins P1 to P8 of the semiconductor device 1. The second column indicates the terminal BOOT, the power supply terminal VIN, the first terminal LX, the ground terminal GND, and the terminals VFB, COMP, EN and SS on the semiconductor substrate 2. The third and fourth columns indicate the wire lengths between the pins P1 to P8 and the respective terminals for a comparative example where the offset amount DW is 0 μm and an example where the offset amount DW is 600 μm.

As shown in Table 1, in the example where the offset amount DW of the semiconductor substrate 2 is 600 μm, the lengths of the wire H1 and the first to third wires H2 to H4 are shorter than those in the comparative example where the offset amount DW is 0 μm. For example, the length of the first wire H2 is 1.58 mm in the comparative example where the offset amount DW is 0 μm, and is reduced to 0.99 mm in the example where the offset amount DW is 600 μm.

Note that while the offset amount DW is set to 600 μm in the example, the offset amount DW is not limited thereto but may be set to DW>0.

The reason why the semiconductor substrate (chip or die) is disposed at the position with the offset amount DW=0 μm as in the comparative example is to mount the semiconductor substrate in the center of the lead frame regardless of the size of the chip (die). In this case, it is difficult to shorten the wires unless a new lead frame (comb) is developed to fit the size of the chip (die).

On the other hand, in the semiconductor device 1 according to the embodiment, the virtual center line DL of the semiconductor substrate 2 is disposed to be offset with respect to the virtual center line IL of the lead frame 3. Therefore, the first to third wires H2 to H4 can be shortened, and the parasitic inductance L can be reduced.

FIGS. 3A and 3B are current waveform diagrams of the first switch element. FIG. 3A shows the case where the offset amount is 0 μm, and FIG. 3B shows the case where the offset amount is 600 μm.

FIGS. 3A and 3B show current waveforms of the first switch element Q1 when the first switch element changes from the OFF state to the ON state, with the horizontal axis indicating time and the vertical axis indicating a current flowing through the first switch element.

In the example where the offset amount DW is 600 μm, the current waveform of the first switch element Q1 converges faster than that in the comparative example where the offset amount DW is 0 μm.

The semiconductor device 1 allows ringing to converge in less time, thereby enabling accurate current detection. For this reason, a high switching frequency is easily realized even in the case of a large current.

Moreover, even in the case of a large current, the DC-to-DC converter 6 can realize a high switching frequency and thus can become more responsive.

Further, the length of the third wire H4 between the pin P4 and the ground terminal GND is also reduced. Accordingly, a parasitic inductance between the pin P4 and the ground terminal GND is also reduced, and thus common mode noise in the ground terminal GND is reduced. As a result, stability and accuracy of the output voltage Vout are improved.

Incidentally, FIG. 2 illustrates the configuration of the controller 14 in a current mode for detecting the current flowing through the first switch element Q1 and controlling the output voltage to be constant. However, the output voltage can also be controlled using a current mode for detecting a current flowing through the second switch element Q2.

FIG. 4 is a circuit diagram illustrating a DC-to-DC converter according to another embodiment.

As shown in FIG. 4, a semiconductor device la has a configuration in which the semiconductor substrate 2 shown in FIG. 2 is replaced by a semiconductor substrate 2 a. A device main body which is not illustrated, first conductors K2 to K4 and second conductors K1 and K5 to K8 are the same as those in the semiconductor device 1 shown in FIG. 1. In addition, first to third wires H2 to H4, wires H1 and H5 to H8, a first terminal LX, a power supply terminal VIN, a ground terminal GND, and terminals BOOT, VFB, COMP, EN and SS are the same as those in the semiconductor device 1 shown in FIGS. 1 and 2.

To be more specific, in the semiconductor device 1 a, a DC-to-DC converter control circuit 30 a is provided on the semiconductor substrate 2 a. The DC-to-DC converter control circuit 30 a has a detector 16 a. Note that the terminal BOOT, the first terminal LX, the power supply terminal VIN and the ground terminal GND are provided on a first side (not shown). The terminals VFB, COMP, EN and SS are provided on the opposite side to the first side.

Further, a virtual center line of the semiconductor substrate 2 a is disposed to be offset to the first side with respect to a virtual center line of a semiconductor substrate mounting part.

In the DC-to-DC converter control circuit 30 a, first and second switch elements Q1 and Q2 and a controller 14 a are provided. The controller 14 a has a configuration in which the detector 16 in the controller 14 shown in FIG. 2 is replaced by the detector 16 a. A driver 15, a voltage generator 17, an error amplifier 18, a comparator 19, a current generator 20 and a parasitic capacitance 21 are the same as those in the controller 14 shown in FIG. 2.

The detector 16 a is a current detector which is connected to the power supply terminal VIN, the first terminal LX and the ground terminal GND, and detects, through the first conductors K2 to K4, a current flowing through the second switch element Q2. The detector 16 a detects an output current of the DC-to-DC converter control circuit 30 a by detecting the current flowing through the second switch element Q2. The detector 16 a has the same configuration as that of the detector 16 shown in FIG. 2.

Further, use of the semiconductor device la can configure a

DC-to-DC converter 6 a in a current mode for detecting and controlling the current flowing through the second switch element Q2.

The DC-to-DC converter 6 a includes the semiconductor device 1 a, a first inductor 7, a first capacitor 8, a feedback circuit 9 and capacitors 11 to 13 and 23.

The DC-to-DC converter 6 a has a configuration in which the semiconductor device 1 in the DC-to-DC converter 6 shown in FIG. 2 is replaced by the semiconductor device 1 a. The first inductor 7, the first capacitor 8, the feedback circuit 9 and the capacitors 11 to 13 and 23 are the same as those in the DC-to-DC converter 6.

The semiconductor device la allows ringing to converge in less time, thereby enabling accurate current detection. For this reason, even in the case of a large current, the DC-to-DC converter 6 a can realize a high switching frequency and thus can become more responsive.

Further, the length of the third wire H4 between the first conductor K4, i.e. the pin P4 and the ground terminal GND is also reduced. Accordingly, a parasitic inductance between the pin P4 and the ground terminal GND is also reduced, and thus common mode noise in the ground terminal GND is reduced. As a result, one-point grounding of the ground terminal GND is ensured, and the stable ground potential improves stability and accuracy of the output voltage Vout.

Such stabilization of the potential of the ground terminal GND is effective also in the case where there is no current detector as in the semiconductor devices 1 and 1 a.

FIG. 5 is a circuit diagram illustrating a DC-to-DC converter according to another embodiment.

As shown in FIG. 5, a semiconductor device 1 b has a configuration in which the semiconductor substrate 2 shown in FIG. 2 is replaced by a semiconductor substrate 2 b. A device main body which is not illustrated, first conductors K2 to K4 and second conductors K1 and K5 to K8 are the same as those in the semiconductor device 1 shown in FIG. 1. In addition, first to third wires H2 to H4, wires H1 and H5 to H8, a first terminal LX, a power supply terminal VIN, a ground terminal GND, and terminals BOOT, VFB, COMP, EN and SS are the same as those in the semiconductor device 1 shown in FIGS. 1 and 2.

To be more specific, in the semiconductor device 1 b, a DC-to-DC converter control circuit 30 b is provided on the semiconductor substrate 2 b. The DC-to-DC converter control circuit 30 b has an error amplifier 18. Note that the terminal BOOT, the first terminal LX, the power supply terminal VIN and the ground terminal GND are provided on a first side (not shown). The terminals VFB, COMP, EN and SS are provided on the opposite side to the first side.

Further, a virtual center line of the semiconductor substrate 2 b is disposed to be offset to the first side with respect to a virtual center line of a semiconductor substrate mounting part (not shown).

In the DC-to-DC converter control circuit 30 b, first and second switch elements Q1 and Q2 and a controller 14 b are provided. The controller 14 b has a configuration in which the detector 16 in the controller 14 shown in FIG. 2 is replaced by a triangle wave generator 22. A driver 15, a voltage generator 17, the error amplifier 18, a comparator 19, a current generator 20 and a parasitic capacitance 21 are the same as those in the controller 14 shown in FIG. 2.

Here, the controller 14 b is connected to the ground terminal GND, to which a ground potential is supplied through the first conductor K4. The semiconductor substrate 2 b is disposed so that the third wire H4 of the first conductor K4 is shortened. As a result, one-point grounding is ensured, and thus common mode noise is reduced. Further, the error amplifier 18 detects and amplifies an error in a voltage fed back to the terminal VFB, and thus the output voltage is stabilized. The error amplifier 18 functions as a detector for detecting a voltage.

The triangle wave generator 22 is a circuit for generating a triangle wave synchronized with a switching frequency of the first and second switch elements Q1 and Q2. An output from the triangle wave generator 22 is inputted to a positive input terminal of the comparator 19 to convert the error voltage into time.

In other words, the controller 14 b controls the first and second switch elements Q1 and Q2 using a PWM signal whose duty ratio varies according to the magnitude of the error voltage.

Further, use of the semiconductor device 1 b can configure a DC-to-DC converter 6 b in a voltage mode.

The DC-to-DC converter 6 b includes the semiconductor device 1 b, a first inductor 7, a first capacitor 8, a feedback circuit 9 and capacitors 11 to 13 and 23.

The DC-to-DC converter 6 b has a configuration in which the semiconductor device 1 in the DC-to-DC converter 6 shown in FIG. 2 is replaced by the semiconductor device 1 b. The first inductor 7, the first capacitor 8, the feedback circuit 9 and the capacitors 11 to 13 and 23 are the same as those in the DC-to-DC converter 6.

The semiconductor device 1 b and the DC-to-DC converter 6 b can reduce common mode noise, thereby improving stability. As a result, a high switching frequency can be realized.

Further, the length of the third wire H4 between the ground terminal GND and the pin P4 is also reduced. Accordingly, a parasitic inductance between the ground terminal GND and the pin P4 is also reduced, and thus common mode noise in the ground terminal GND is reduced. As a result, stability and accuracy of the output voltage Vout are improved.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions. 

1. A semiconductor device comprising: a semiconductor substrate including a DC-to-DC converter control circuit, and having a power supply terminal on a first side of the semiconductor substrate and an other terminal on a opposite side to the first side; a first wire electrically connected the power supply terminal; and a second wire electrically connected the other terminal, a length of the second wire being longer than a length of the first wire.
 2. The device according to claim 1, wherein the semiconductor substrate is disposed so that a virtual center line of the semiconductor substrate is offset to the first side with respect to a virtual center line of a mounting portion.
 3. The device according to claim 1, wherein the semiconductor substrate has a first terminal and a ground terminal, the both terminal are provided on the first side, the DC-to-DC converter control circuit includes: a first switch element electrically connected between the power supply terminal and the first terminal; and a controller configured to control the first switch element, and the controller includes: a current detector configured to detect a current flowing through a first portion configured to be supplied at least one of a current and a voltage; and an error amplifier configured to detect an error in a voltage fed back to the terminal via a second portion configured to be input and output a signal with reference to the ground terminal.
 4. The device according to claim 3, wherein the current detector detects the current flowing through the first switch element.
 5. The device according to claim 3, further comprising a third wire electrically connected the first terminal, and a length of the third wire is shorter than the length of the second wire.
 6. The device according to claim 5, wherein the DC-to-DC converter control circuit includes a second switch element connected to the first switch element, and the DC-to-DC converter control circuit outputs, through the third wire, a voltage changing between a power supply potential and a ground potential.
 7. The device according to claim 6, wherein the current detector detects the current flowing through the second switch element.
 8. The device according to claim 6, wherein the first wire supplies a current flowing through a connection point between the first and second switch elements.
 9. The device according to claim 3, further comprising a fourth wire electrically connected the ground terminal, a length of the fourth wire is shorter than the length of the second wire.
 10. The device according to claim 9, wherein the fourth wire supplies a ground potential to the DC-to-DC converter control circuit.
 11. The device according to claim 2, further comprising a device main body, the mounting portion is provided on the device main body.
 12. The device according to claim 11, wherein the device main body includes: a first portion configured to be supplied at least one of a current and a voltage; and a second portion configured to be input and output a signal, the first wire is electrically connected between the power supply terminal and the first portion, and the second wire is electrically connected between the other terminal and the second portion.
 13. The device according to claim 1, wherein the first wire supplies a power supply potential to the DC-to-DC converter control circuit.
 14. The device according to claim 1, wherein the DC-to-DC converter control circuit has a detector to detect at least one of a current flowing through the first wire and a voltage supplied to the first wire.
 15. The device according to claim 14, wherein the detector is a current detector to detect an output current of the DC-to-DC converter control circuit.
 16. The device according to claim 14, wherein the detector is a voltage detector to detect a voltage fed back to the DC-to-DC converter control circuit.
 17. The device according to claim 14, wherein the first wire supplies a power supply potential to the detector.
 18. A DC-to-DC converter comprising: a semiconductor device including a semiconductor substrate, a first wire, and a second wire, the semiconductor substrate including a DC-to-DC converter control circuit, and having a power supply terminal on a first side of the semiconductor substrate and an other terminal on a opposite side to the first side, the first wire being electrically connected the power supply terminal, the second wire being electrically connected the other terminal, and a length of the second wire being longer than a length of the first wire; a first inductor connected to an output of the DC-to-DC converter control circuit; and a first capacitor connected between the first inductor and the ground.
 19. The converter according to claim 18, wherein the semiconductor substrate is disposed so that a virtual center line of the semiconductor substrate is offset to the first side with respect to a virtual center line of a mounting portion.
 20. The converter according to claim 18, wherein the semiconductor substrate has a first terminal and a ground terminal, the both terminal are provided on the first side, the DC-to-DC converter control circuit includes: a first switch element electrically connected between the power supply terminal and the first terminal; and a controller configured to control the first switch element, and the controller includes: a current detector configured to detect a current flowing through a first portion configured to be supplied at least one of a current and a voltage; and an error amplifier configured to detect an error in a voltage fed back to the terminal via a second portion configured to be input and output a signal with reference to the ground terminal. 